edisoncarter at GTASanAndreas.net has recently been finding new cheat codes by "wiring up a game pad to a PC's parallel port using optocouplers". Yes it's highly complex.

Cars Fly

But the controls are like flying a normal plane.

Square, Down, L2, Up, L1, Circle, Up, X, Left

Fast/Rare cars appear regularly

Up, L1, R1, Up, Right, Up, X, L2, X, L1

Full Weapon Aiming Whilst Driving

Aim and shoot at passing pedestrians/vehicles, as your gang would do whilst in a car

Up, Up, Square, L2, Right, X, R1, Down, R2, Circle

All taxis have nitrous and bunny hops

Horn to bunny hop

Up, X, Triangle, X, Triangle, X, Square, R2, Right

Spawn a Bulldozer

R2, L1, L1, Right, Right, Up, Up, L1, Left

Reduced Traffic

Very few cars on the streets and no pedestrians

X, Down, Up, R2, Down, Triangle, L1, Triangle, Left

Orange Sky

This cheat freezes the clock at 21:00 after a rapid whether change the skies will be orange.

Left, Left, L2, R1, Right, Square, Square, L1, L2, X

Gangs Control the City

This cheat will empty the streets leaving just gang members and vehicles within the gang territories

L2, Up, R1, R1, Left, R1, R1, R2, Right, Down

Infinite Lung Capacity

Now you will never drown

Down, Left, L1, Down, Down, R2, Down, L2, Down

The cheats page will be updated shortly with these new codes.